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NAME ___________________________ PERIOD ____ DATE ______ “Endler’s Guppies” -- A Reading on Scientific Inquiry The excerpt you are to read for this assignment is from the book, The Beak of the Finch: A Story of Evolution in our Time. Most of this book focuses on the work of Peter and Rosemary Grant who have been studying the finches on the Galapagos Islands off of South America. However, this eight-page excerpt describes the work of John Endler with guppies in northern South America and some islands in the Caribbean Sea. The reading will not only provide a wonderful example of how natural selection operates, but it will also describe how a scientist does his work. The questions below will guide you through the reading and help you to focus on ways in which John Endler tried to answer some basic questions about the evolution of guppies. One thing you will be asked to do throughout the assignment is to ask questions of the text you are reading. Asking questions is how most of scientific exploration begins. As you ask questions you are doing exactly what scientists do every day. Prior Knowledge Before you begin this reading, you should make sure you understand the following ideas: Natural selection is the process by which individuals that are better suited to their environment survive and reproduce most successfully. Sexual selection is a special form of natural selection based on an organism’s ability to mate. Part I Read paragraphs 1-10 1. Pose a question you have about the description of the guppies given in paragraph three. 2. Make a hypothesis about why only male guppies have spots. 3. What appears to be the function of the spots on the guppies? 4. Why is natural selection more intense in the lower reaches of the stream? 5. Paragraph ten describes in some detail one of the first things Endler did once he decided to study the guppies. What did he do? Why did he do this? Summary: The first two-pages of this reading introduce you to John Endler and the guppies of Venezuela and three Caribbean islands. How would you describe to someone how Endler started his research on the guppies? Part II Read paragraphs 11-15 6. After Endler accurately recorded in great detail the color, size, and position of the spots on the male guppies, what pattern did his analysis discover? 7. What conclusion does Endler come to in paragraph 14? 8. In the next paragraph, Endler poses an important question. Before moving on in the reading, how would you respond to this question? Part III Read paragraphs 16-21 9. How does Endler answer the question posed in paragraph 15? 10. How do male guppies with small dots attract females and yet seem to escape their predators? 11. What is an interesting pattern of color that seems to support the idea that natural selection is at work in the guppies? 11. What questions do you have at this point in the reading? Part IV Read paragraphs 22-33 13. Paragraphs 22-26 describe the evolutionary experiment which Endler set up in his laboratory at Princeton University in New Jersey. What important steps did Endler take in designing his experiment? 14. What did he predict would happen? 15. Paragraph 30 describes another important thing scientists must do if they are to successfully test their hypotheses. What is it? 16. Paragraph 33 raises a doubt about Endler’s results—what is the doubt? Do you think it is reasonable? Explain. Part V Read paragraphs 34-40 17. Describe briefly the experiment in nature which Endler designed? 18. How does natural selection and sexual selection contribute to the great diversity of patterns observed in nature? 19. What is Endler now doing to try to more deeply understand how the guppies evolve? 20. As you finish this reading, what questions do you still have about how evolution works in guppies? 21. Take one of the questions you posed in #20. How would you go about researching this question? Written by Larry Wakeford as part of Project ARISE, a SEPA-funded project of the National Institutes of Health, 2008.